AbstractQueuedLongSynchronizer

public abstract class AbstractQueuedLongSynchronizer extends AbstractOwnableSynchronizer
implements Serializable

A version of AbstractQueuedSynchronizer in which synchronization state is maintained as a long. This class has exactly the same structure, properties, and methods as AbstractQueuedSynchronizer with the exception that all state-related parameters and results are defined as long rather than int. This class may be useful when creating synchronizers such as multilevel locks and barriers that require 64 bits of state.

See AbstractQueuedSynchronizer for usage notes and examples.

Nested Class Summary

class

AbstractQueuedLongSynchronizer.ConditionObject

Condition implementation for a AbstractQueuedLongSynchronizer serving as the basis of a Lock implementation.

Protected Constructor Summary

AbstractQueuedLongSynchronizer() Creates a new AbstractQueuedLongSynchronizer instance with initial synchronization state of zero.

Public Method Summary

final void	acquire(long arg) Acquires in exclusive mode, ignoring interrupts.
final void	acquireInterruptibly(long arg) Acquires in exclusive mode, aborting if interrupted.
final void	acquireShared(long arg) Acquires in shared mode, ignoring interrupts.
final void	acquireSharedInterruptibly(long arg) Acquires in shared mode, aborting if interrupted.
final Collection<Thread>	getExclusiveQueuedThreads() Returns a collection containing threads that may be waiting to acquire in exclusive mode.
final Thread	getFirstQueuedThread() Returns the first (longest-waiting) thread in the queue, or null if no threads are currently queued.
final int	getQueueLength() Returns an estimate of the number of threads waiting to acquire.
final Collection<Thread>	getQueuedThreads() Returns a collection containing threads that may be waiting to acquire.
final Collection<Thread>	getSharedQueuedThreads() Returns a collection containing threads that may be waiting to acquire in shared mode.
final int	getWaitQueueLength(AbstractQueuedLongSynchronizer.ConditionObject condition) Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer.
final Collection<Thread>	getWaitingThreads(AbstractQueuedLongSynchronizer.ConditionObject condition) Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer.
final boolean	hasContended() Queries whether any threads have ever contended to acquire this synchronizer; that is, if an acquire method has ever blocked.
final boolean	hasQueuedPredecessors() Queries whether any threads have been waiting to acquire longer than the current thread.
final boolean	hasQueuedThreads() Queries whether any threads are waiting to acquire.
final boolean	hasWaiters(AbstractQueuedLongSynchronizer.ConditionObject condition) Queries whether any threads are waiting on the given condition associated with this synchronizer.
final boolean	isQueued(Thread thread) Returns true if the given thread is currently queued.
final boolean	owns(AbstractQueuedLongSynchronizer.ConditionObject condition) Queries whether the given ConditionObject uses this synchronizer as its lock.
final boolean	release(long arg) Releases in exclusive mode.
final boolean	releaseShared(long arg) Releases in shared mode.
String	toString() Returns a string identifying this synchronizer, as well as its state.
final boolean	tryAcquireNanos(long arg, long nanosTimeout) Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses.
final boolean	tryAcquireSharedNanos(long arg, long nanosTimeout) Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses.

Protected Method Summary

final boolean	compareAndSetState(long expect, long update) Atomically sets synchronization state to the given updated value if the current state value equals the expected value.
final long	getState() Returns the current value of synchronization state.
boolean	isHeldExclusively() Returns true if synchronization is held exclusively with respect to the current (calling) thread.
final void	setState(long newState) Sets the value of synchronization state.
boolean	tryAcquire(long arg) Attempts to acquire in exclusive mode.
long	tryAcquireShared(long arg) Attempts to acquire in shared mode.
boolean	tryRelease(long arg) Attempts to set the state to reflect a release in exclusive mode.
boolean	tryReleaseShared(long arg) Attempts to set the state to reflect a release in shared mode.

Inherited Method Summary

From class java.util.concurrent.locks.AbstractOwnableSynchronizer

final Thread	getExclusiveOwnerThread() Returns the thread last set by setExclusiveOwnerThread, or null if never set.
final void	setExclusiveOwnerThread(Thread thread) Sets the thread that currently owns exclusive access.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Protected Constructors

protected AbstractQueuedLongSynchronizer ()

Creates a new AbstractQueuedLongSynchronizer instance with initial synchronization state of zero.

Public Methods

public final void acquire (long arg)

Acquires in exclusive mode, ignoring interrupts. Implemented by invoking at least once tryAcquire(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(long) until success. This method can be used to implement method Lock.lock().

Parameters

arg	the acquire argument. This value is conveyed to tryAcquire(long) but is otherwise uninterpreted and can represent anything you like.

public final void acquireInterruptibly (long arg)

Acquires in exclusive mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquire(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(long) until success or the thread is interrupted. This method can be used to implement method Lock.lockInterruptibly().

Parameters

arg	the acquire argument. This value is conveyed to tryAcquire(long) but is otherwise uninterpreted and can represent anything you like.

Throws

InterruptedException	if the current thread is interrupted

public final void acquireShared (long arg)

Acquires in shared mode, ignoring interrupts. Implemented by first invoking at least once tryAcquireShared(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(long) until success.

Parameters

arg	the acquire argument. This value is conveyed to tryAcquireShared(long) but is otherwise uninterpreted and can represent anything you like.

public final void acquireSharedInterruptibly (long arg)

Acquires in shared mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquireShared(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(long) until success or the thread is interrupted.

Parameters

arg	the acquire argument. This value is conveyed to tryAcquireShared(long) but is otherwise uninterpreted and can represent anything you like.

Throws

InterruptedException	if the current thread is interrupted

public final Collection<Thread> getExclusiveQueuedThreads ()

Returns a collection containing threads that may be waiting to acquire in exclusive mode. This has the same properties as getQueuedThreads() except that it only returns those threads waiting due to an exclusive acquire.

Returns

• the collection of threads

public final Thread getFirstQueuedThread ()

Returns the first (longest-waiting) thread in the queue, or null if no threads are currently queued.

In this implementation, this operation normally returns in constant time, but may iterate upon contention if other threads are concurrently modifying the queue.

Returns

• the first (longest-waiting) thread in the queue, or null if no threads are currently queued

public final int getQueueLength ()

Returns an estimate of the number of threads waiting to acquire. The value is only an estimate because the number of threads may change dynamically while this method traverses internal data structures. This method is designed for use in monitoring system state, not for synchronization control.

Returns

• the estimated number of threads waiting to acquire

public final Collection<Thread> getQueuedThreads ()

Returns a collection containing threads that may be waiting to acquire. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive monitoring facilities.

Returns

• the collection of threads

public final Collection<Thread> getSharedQueuedThreads ()

Returns a collection containing threads that may be waiting to acquire in shared mode. This has the same properties as getQueuedThreads() except that it only returns those threads waiting due to a shared acquire.

Returns

• the collection of threads

public final int getWaitQueueLength (AbstractQueuedLongSynchronizer.ConditionObject condition)

Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer. Note that because timeouts and interrupts may occur at any time, the estimate serves only as an upper bound on the actual number of waiters. This method is designed for use in monitoring system state, not for synchronization control.

Parameters

condition	the condition

Returns

• the estimated number of waiting threads

Throws

IllegalMonitorStateException	if exclusive synchronization is not held
IllegalArgumentException	if the given condition is not associated with this synchronizer
NullPointerException	if the condition is null

public final Collection<Thread> getWaitingThreads (AbstractQueuedLongSynchronizer.ConditionObject condition)

Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order.

Parameters

condition	the condition

Returns

• the collection of threads

Throws

IllegalMonitorStateException	if exclusive synchronization is not held
IllegalArgumentException	if the given condition is not associated with this synchronizer
NullPointerException	if the condition is null

public final boolean hasContended ()

Queries whether any threads have ever contended to acquire this synchronizer; that is, if an acquire method has ever blocked.

In this implementation, this operation returns in constant time.

Returns

• true if there has ever been contention

public final boolean hasQueuedPredecessors ()

Queries whether any threads have been waiting to acquire longer than the current thread.

An invocation of this method is equivalent to (but may be more efficient than):

 getFirstQueuedThread() != Thread.currentThread()
   && hasQueuedThreads()

Note that because cancellations due to interrupts and timeouts may occur at any time, a true return does not guarantee that some other thread will acquire before the current thread. Likewise, it is possible for another thread to win a race to enqueue after this method has returned false, due to the queue being empty.

This method is designed to be used by a fair synchronizer to avoid barging. Such a synchronizer's tryAcquire(long) method should return false, and its tryAcquireShared(long) method should return a negative value, if this method returns true (unless this is a reentrant acquire). For example, the tryAcquire method for a fair, reentrant, exclusive mode synchronizer might look like this:

 protected boolean tryAcquire(int arg) {
   if (isHeldExclusively()) {
     // A reentrant acquire; increment hold count
     return true;
   } else if (hasQueuedPredecessors()) {
     return false;
   } else {
     // try to acquire normally
   }
 }

Returns

• true if there is a queued thread preceding the current thread, and false if the current thread is at the head of the queue or the queue is empty

public final boolean hasQueuedThreads ()

Queries whether any threads are waiting to acquire. Note that because cancellations due to interrupts and timeouts may occur at any time, a true return does not guarantee that any other thread will ever acquire.

In this implementation, this operation returns in constant time.

Returns

• true if there may be other threads waiting to acquire

public final boolean hasWaiters (AbstractQueuedLongSynchronizer.ConditionObject condition)

Queries whether any threads are waiting on the given condition associated with this synchronizer. Note that because timeouts and interrupts may occur at any time, a true return does not guarantee that a future signal will awaken any threads. This method is designed primarily for use in monitoring of the system state.

Parameters

condition	the condition

Returns

• true if there are any waiting threads

Throws

IllegalMonitorStateException	if exclusive synchronization is not held
IllegalArgumentException	if the given condition is not associated with this synchronizer
NullPointerException	if the condition is null

public final boolean isQueued (Thread thread)

Returns true if the given thread is currently queued.

This implementation traverses the queue to determine presence of the given thread.

Parameters

thread	the thread

Returns

• true if the given thread is on the queue

Throws

NullPointerException	if the thread is null

public final boolean owns (AbstractQueuedLongSynchronizer.ConditionObject condition)

Queries whether the given ConditionObject uses this synchronizer as its lock.

Parameters

condition	the condition

Returns

• true if owned

Throws

NullPointerException	if the condition is null

public final boolean release (long arg)

Releases in exclusive mode. Implemented by unblocking one or more threads if tryRelease(long) returns true. This method can be used to implement method Lock.unlock().

Parameters

arg	the release argument. This value is conveyed to tryRelease(long) but is otherwise uninterpreted and can represent anything you like.

Returns

• the value returned from tryRelease(long)

public final boolean releaseShared (long arg)

Releases in shared mode. Implemented by unblocking one or more threads if tryReleaseShared(long) returns true.

Parameters

arg	the release argument. This value is conveyed to tryReleaseShared(long) but is otherwise uninterpreted and can represent anything you like.

Returns

• the value returned from tryReleaseShared(long)

public String toString ()

Returns a string identifying this synchronizer, as well as its state. The state, in brackets, includes the String "State =" followed by the current value of getState(), and either "nonempty" or "empty" depending on whether the queue is empty.

Returns

• a string identifying this synchronizer, as well as its state

public final boolean tryAcquireNanos (long arg, long nanosTimeout)

Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses. Implemented by first checking interrupt status, then invoking at least once tryAcquire(long), returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(long) until success or the thread is interrupted or the timeout elapses. This method can be used to implement method Lock.tryLock(long, TimeUnit).

Parameters

arg	the acquire argument. This value is conveyed to tryAcquire(long) but is otherwise uninterpreted and can represent anything you like.
nanosTimeout	the maximum number of nanoseconds to wait

Returns

• true if acquired; false if timed out

Throws

InterruptedException	if the current thread is interrupted

public final boolean tryAcquireSharedNanos (long arg, long nanosTimeout)

Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses. Implemented by first checking interrupt status, then invoking at least once tryAcquireShared(long), returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(long) until success or the thread is interrupted or the timeout elapses.

Parameters

arg	the acquire argument. This value is conveyed to tryAcquireShared(long) but is otherwise uninterpreted and can represent anything you like.
nanosTimeout	the maximum number of nanoseconds to wait

Returns

• true if acquired; false if timed out

Throws

InterruptedException	if the current thread is interrupted

Protected Methods

protected final boolean compareAndSetState (long expect, long update)

Atomically sets synchronization state to the given updated value if the current state value equals the expected value. This operation has memory semantics of a volatile read and write.

Parameters

expect	the expected value
update	the new value

Returns

• true if successful. False return indicates that the actual value was not equal to the expected value.

protected final long getState ()

Returns the current value of synchronization state. This operation has memory semantics of a volatile read.

Returns

• current state value

protected boolean isHeldExclusively ()

Returns true if synchronization is held exclusively with respect to the current (calling) thread. This method is invoked upon each call to a non-waiting AbstractQueuedLongSynchronizer.ConditionObject method. (Waiting methods instead invoke release(long).)

The default implementation throws UnsupportedOperationException. This method is invoked internally only within AbstractQueuedLongSynchronizer.ConditionObject methods, so need not be defined if conditions are not used.

Returns

• true if synchronization is held exclusively; false otherwise

Throws

UnsupportedOperationException	if conditions are not supported

protected final void setState (long newState)

Sets the value of synchronization state. This operation has memory semantics of a volatile write.

Parameters

newState	the new state value

protected boolean tryAcquire (long arg)

Attempts to acquire in exclusive mode. This method should query if the state of the object permits it to be acquired in the exclusive mode, and if so to acquire it.

This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread. This can be used to implement method Lock.tryLock().

The default implementation throws UnsupportedOperationException.

Parameters

arg	the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns

• true if successful. Upon success, this object has been acquired.

Throws

IllegalMonitorStateException	if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
UnsupportedOperationException	if exclusive mode is not supported

protected long tryAcquireShared (long arg)

Attempts to acquire in shared mode. This method should query if the state of the object permits it to be acquired in the shared mode, and if so to acquire it.

This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread.

The default implementation throws UnsupportedOperationException.

Parameters

arg	the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns

• a negative value on failure; zero if acquisition in shared mode succeeded but no subsequent shared-mode acquire can succeed; and a positive value if acquisition in shared mode succeeded and subsequent shared-mode acquires might also succeed, in which case a subsequent waiting thread must check availability. (Support for three different return values enables this method to be used in contexts where acquires only sometimes act exclusively.) Upon success, this object has been acquired.

Throws

IllegalMonitorStateException	if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
UnsupportedOperationException	if shared mode is not supported

protected boolean tryRelease (long arg)

Attempts to set the state to reflect a release in exclusive mode.

This method is always invoked by the thread performing release.

The default implementation throws UnsupportedOperationException.

Parameters

arg	the release argument. This value is always the one passed to a release method, or the current state value upon entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns

• true if this object is now in a fully released state, so that any waiting threads may attempt to acquire; and false otherwise.

Throws

IllegalMonitorStateException	if releasing would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
UnsupportedOperationException	if exclusive mode is not supported

protected boolean tryReleaseShared (long arg)

Attempts to set the state to reflect a release in shared mode.

This method is always invoked by the thread performing release.

The default implementation throws UnsupportedOperationException.

Parameters

arg	the release argument. This value is always the one passed to a release method, or the current state value upon entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns

• true if this release of shared mode may permit a waiting acquire (shared or exclusive) to succeed; and false otherwise

Throws

IllegalMonitorStateException	if releasing would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
UnsupportedOperationException	if shared mode is not supported